Custom Fields

Just getting started with MMEX and not understanding how to use custom fields. I opened the new window and clicked the custom fields button at the bottom, then in the Custom fields window I clicked the add/edit/delete button, added a new custom field, then closed the Personliaze custom fields and Custom Fields dialogs. I thought perhaps the custom field would then be added to the New Transaction dialog but it wasn't. SO then I clicked the New Transaction custom fields button again and in the resulting dialog, my custom field name was listed (partially obscured by the Close button) but it wasn't clickable and I couldn't find any way to enter a value for it.

There doesn't seem to be any documentation for this feature so hoping can describe how to use it.